1. Field of the Invention
The present invention is related to a power supply and related DC-DC converter, and more particularly, to a power supply and related DC-DC converter capable of reducing ripples on output voltages of the power supply by synchronizing clocks of different DC-DC converters.
2. Description of the Prior Art
An electronic device usually includes various components requiring different operating voltages. In order to provide the operating voltages, a power supply includes multiple DC-DC (direct current) voltage converting circuits, such as a buck (step down) converter or boost (step up) converter, utilized for adjusting (step up or step down) voltage levels and stabilizing the adjusted voltages at specific default levels.
Please refer to FIG. 1, which is a schematic diagram of a power supply 10 of the prior art. The power supply 10 includes a rectifier 100, a front-stage DC-DC converter 102 and back-stage DC-DC converters 104, 106. The rectifier 100 converts an alternating current (AC) voltage VAC provided by an AC voltage source 108 into a direct current (DC) voltage VDC. The front-stage DC-DC converter 102 adjusts level of the DC voltage VDC to generate a major output voltage VOUT_M. The back-stage DC-DC converters 104, 106 respectively generate minor output voltages VOUT_m1, VOUT_m2 based on the major output voltage VOUT_M to provide different voltage levels. For example, if the power supply 10 is a power supply conforming to an ATX (Advanced Technology Extended) power standard, the rectifier 100 converts an 110V AC household voltage into an 110V DC voltage. Next, the front-stage DC-DC converter 102 converts the 110V DC voltage into a 12V DC voltage. Finally, the back-stage DC-DC converters 104, 106 respectively convert the 12V DC voltage into 5V and 3.3V DC voltages. As a result, 12V, 5V or 3.3V can be applied to electronic components based upon specific power requirements.
In general, the front-stage DC-DC converter 102 and the back-stage DC-DC converters 104, 106 are switching DC-DC converters. That is, the front-stage DC-DC converter 102 and the back-stage DC-DC converters 104, 106 generate sawtooth wave signals by oscillators to indicate switching timing of a charging/discharging path. In other words, the front-stage DC-DC converter 102 and the back-stage DC-DC converters 104, 106 generate various output voltage levels by adjusting a duty cycle of the charging/discharging path.
However, due to undesired factors like manufacturing process defects, physical properties of materials, etc., parasitic components naturally exist in the power supply 10, and lead to coupling effects between the output voltages VOUT_M, VOUT_m1, VOUT_m2 with undesired ripples, as illustrated in FIG. 2. The ATX power standard defines tolerance of amplitudes of ripples within a small range. That is, if the power supply 10 cannot effectively attenuate the ripples, related product yield drops dramatically. For that reason, the power supply 10 is installed with filters at output ends to reduce amplitudes of the ripples. However, extra hardware implies extra cost.
Therefore, reduction of ripples on output voltages of a power supply has been a major focus of the industry.